Mounting for tuning elements



12, 1940.- I .1. c. SMITH MOUNTING FOR TUNING murmurs Filed Aug. 31, 1935 6 PRIOR 4R Patented Mar. 12, 1940 UNITED STATES PATENT OFFICE MOUNTING FOR TUNING ELEMENTS Jerome C. Smith, Merchantville, N. J assignor to Radio Corporation of America, a corporation of Delaware This invention relates to radio apparatus, particularly to tuning elements and has special reference to improvements in non-microphonic mountings for devices of this general type. While the invention will be described in connection with capacity type tuning elements it is to be understood that the invention is not limited to such application as the disclosure in this respect is merely illustrative for purposes of explaining the inventive concept.

The specification and claims defining the invention will be best understood by reference to the accompanying drawing wherein? Fig. 1 is an end elevation partly in section of a tuning element mounted in accordance with the prior art; it is included for the purpose of i1 lustrating the problem involved,

Fig. 2 is an end elevation partly in section of a tuning element assembly mounted in accordance 20 with the present invention,

Fig. 3 is a top plan view of the invention as embodied in Fig. 2 showing the assembly suspended or cradled at three points,

Fig. 4 is a fragmentary top plan view of a modi 25 fied form of the invention,

Fig. 5 is a fragmentary elevation showing a modified form of vibration-insulating member,

Fig. 6 is a front elevation partly in section of another embodiment of the invention.

30 Radio installations, especially modern high frequency receivers, are extremely sensitive in their performance to mechanical shocks and jars. Such disturbances tend to set up microphonic and/or other parasitic tremors which when am- 35 plified and translated by the various electric instruments in the set are acoustically or visually noticeable, as the case may be, in the output device.

In an effort to obviate these spurious vibrations 40 early experimenters provided chassis, panels and bases resiliently mounted, as on springs or on rubber or felt. Such expedients, however, were found less satisfactory than desirable since, while partially effective in insulating the set from ex- 45 ternal forces, they have but little damping effect upon vibrations arising or appearing in the apparatus itself. As recorded by Taylor and White (U. S. P. 1,669,217, filed October 1'7, 1925, page 1, lines 65-70) it was observed that distortion in- 50 creased with the frequency to which the ap paratus was tuned and a large part of the trouble was traced to vibration of the condenser plates. Taylor and White found that microphonic noises in the receiving circuits were substantially re- 65 duced by providing, in addition to the usual re-' silient set-mountings, a tuning arrangement including condenser plates made of low resistance material having a natural period of vibration below or above the audible range.

Roberts and Van Dyck working independently, 5

Thus, referring to Fig. 1, which is an end view of a tuning element mounted in accordance with the prior art and is included for purposes of illustrating the problem involved. This figure shows a condenser plate I disposed for rotation upon a rotor shaft 2. The shaft is carried, usually cif center, by an end plate 3 and the entire assembly supported by rubber grommets 4 and 5. The grommets are fixed to the chassis or base 6 of the set as by screws 1 which extend through washers 4' 5' on the underside of the base 6.

It will be observed in connection with this typical prior art installation that if there is a tendency for the assembly to move up and down, as at A (due to chassis vibration as caused by a loudspeaker, not shown) the weight of the assembly is concentrated over one or the other of the supports, permitting one corner to rise and fall in step with the disturbance, thus twisting one end plate with respect to the other and causing a shift in the condenser plate placement.

Similarly if there is a tendency to make this unit shift lengthwise (i. e. perpendicular to the plane of the paper) near the top as at B, the rotor I together with the upper part of the frame may start vibrating slightly, which will cause a change in capacity in the lower section 0 since the stator plates are there relatively stationary. Further, since the shaft 2 is off center, crosswise vibration, as shown by arrow D, has a leverage on the supporting rubber grommets 4-5 which will concentrate the movement adjacent the top of the assembly.

Another and very real disadvantage of prior art mountings especially apparent in modern receivers where the drive mechanism is rigidly fixed on the chassis and the condenser is flexibly mounted-is indicated by the arrows E-E showing the rocking motion which will usually accompany movement of the tuning knob. This struction of the assembly.

'1 of beam H rocking movement produces an effect which is very similar to back-lash and makes accurate tuning difficult.

A principlal object of the present invention is to provide a supporting arrangement for tuning elements and the like obviating the above and other disadvantages inherent in prior art mountings.

Another object of the invention is to provide a mounting arrangement for tuning elements wherein the axis of support lies in a plane adjacent the center of gravity of the elements supported.

Another object is to provide a mounting for tuning elements wherein the elements to be supported are effectively cradled against vibrationproducing stresses and strains.

Referring now to Figs. 2 and 3 which show a preferred embodiment of the invention as applied to an assembly of tuning elements of the capacity type. The assembly itself is provided with a front end plate 211 and a rear end plate 23, each jcurnaled to accommodate a shaft 25 upon which the: rotor plates 21 are mounted. Beds 3! and 33 support the stator plates 29 and rods 35 and 31' carry a number of shielding plates dd 11 idity to-the assembly.

In accoi dance with the principle of the inven tion the as embly is suspended, as from a bridge, at points in a plane substantially adjacent center of gravity; Thev center of gravity will. usually lie in a plane. adjacent the mid-section of the tuning assembly, its exact position depending, of course, upon the particular type and con The supporting structure employed in carrying the invention into effc t may comprise an L beam M extending and preferably projecting beyond the opposite sideedges of the front face plate 2!. Plate 2% lies in face to face relation with the perpendicular arm Ma of l. beam M and is fixed thereto as by means. of rivets it-45 arranged in spaced 1' ion on opposite sides of the rotor shaft 25. he projecting portions of the horizontal arm i lb rest upon grommets 437-45 of rubber or other vibration insulating material carried respectively by risers. orstubs Ext-53 and are secured thereto as by means of nuts 5! and to threaded on the. end section of the studs. studs are secured to the base 5t on its underside by means of rivets 55 and 57.

The studs 5l'53s are preferably spaced apart a distance. greater than that required to accommodate the tuning assembly. As shown in Figs. 2 and 3 the number of supporting points, and hence t number of studs may be limited, in the inter sts of economy, to the minimum number recu to define the plane in which the assembly is supported, i. e. three. In these figures the th' e grommet. is designated 59 and the stud 6i. Therear end plate lit-is provided with an L flange member one arm. of which is fixed to its outer surface and the other is secured to its grommet 2;,in a manner similar to that described connection with the front plate 2 t.

If desired the tuning assembly may be suspended between two pairs of supporting studs, in which case, as indicated in Fig. 4 the rear mounting arrangement including the beam Ml spanning the resilient grommets Mi -59 may be sin: in all respects to that previously described.

It is not always necessary to mount the bridging L beams directly upon the resilient members, they may, as shown in Fig. 5, be connected di rectly to the metal studs i253 and the studs insulated from extraneous vibrations by grommets 269 adjacent the base 54.

Fig. 6 shows another embodiment of the invention wherein the tuning element assembly 2| is suspended from its mid-section on an L beam 45 which bridges an orifice 354a in the base 354. The bridging member rests upon rubber grommets M L-3&9 which are fixed directly to the base by short studs 35l-353. The studs are insulated from the underside of the base by washers 255i As in the other embodiments the assembly is suspended in a plane, substantially adjacent its center of gravity. Here, however, the well formed by the orifice 254a; accommodates the lower part of the unit and the plane in which it is supported coincides substantially with the plane of the base 3%.

The improved operating performance of condensers mounted in accordance with the present invention may be attributed in part to the fact that any vibrations which may be transmitted tlfrrough the supports tend to move the rotor and stator plates together so that they are not displaced with respect to each other and consequently produce little or no change in capacitance. Further, since the rubber feet p1- vide a relatively wider base than hitherto emd, torsional stability is augmented and back- 1 substantially obviated.

In carrying the invention into effect various changes in be made in the above described embodiments of the invention without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In cornbination in radio apparatus, a variable tu-ning element, a chassis having a base, means independent of supporting structure for said chassis for supporting said tuning element on said chassis base, said means being attached to said variable tuning element adjacent the level of the center of gravity thereof and comprising vibration damping means interposed between said tut element and base.

The invention as set forth in claim 1 wherein the means for supporting said tuning element includes a plurality of vibration damping elements disposed-adjacent the level of the center of gravity of said tuning element.

3. The invention as set forth in claim 1 wherein the plane which said tuning element is supported coincides substantially with the plane of said chassisbase.

4. In combination in radio apparatus, a variable tuning element, a chassis having a base, and means including a resilient member intermediate said base tuning element for supporting said tuning element adjacent the level of the center of gravity thereof, said means constituting the sole support for said tuning element and being independent of supporting structure for said chassis.

5. In. combination in radio apparatus, a variable tuning element constituted by a pair of endplates having a plurality of interposed condenser elements and a shaft for said elements journaled centrally in said plates and projecting therefrom, a chassis having a base, means independent of supporting structure for said chassis for supporting said tuning element on said chassis base, said comprising a plurality of spaced studs on said base, support members fixed to said end plates and to said studs adjacent the l vel containing the center of gravity of said tuning element,andvibration damping elements fixed to said studs intermediate said support members and said base, said studs being spaced apart a distance substantially greater than that required to accommodate said tuning element and being substantially equally spaced from said tuning shaft and from the points whereat said support members are affixed to said end plates.

6. In combination in radio apparatus, a variable tuning element, a chassis having a base, means independent of supporting structure for said chassis for supporting said tuning element on said chassis base, said means comprising a plurality of spaced studs on said base, support members fixed to said tuning element and to said studs adjacent the level containing the center of gravity of said tuning element and vibration damping elements fixed to said studs intermediate said support members and said base.

7. The combination set forth in claim 6 wherein said studs are spaced apart a distance substantially greater than that required to accommodate said tuning element.

8. The combination set forth in claim 6 wherein the number of studs corresponds to the minimum number of points required to define the plane of support for said tuning element.

9. The combination set forth in claim 6 wherein four studs are provided, the studs of each pair having support members common thereto.

10. The combination set forth in claim 6 wherein the center of gravity of said tuning element falls on a through a point two of said stu ll. The comb 1 on Mt forth in claim 6 wherein said support members are atftl ed to said tuning element at po its substantially equally distant from a point init'iway between two oi said studs.

12. The combination set forth in claim 6 wherein said tuning element is suspended adjacent points substantially midway between the top and bottom thereof 13. The combination set forth in claim 6 wherein vibration damping elements are interposed between said studs and support members.

14. The combination set forth in claim 6 wherein vibration damping means are interposed between said base and said studs.

15. A variable tuning device comprising rotor and stator elements, means including an end plate for maintaining said elements in alignment, and means comprising a pair of outwardly extending oppositely located arms for mounting said device, the outer extremities of: said arms 1:-

being spaced apart a distance substantially greater than is necessary to accommodate said device.

JEROME C. SMITH. 

